Studies on Fungicides — III 33 



In still another experiment, designed more or less to duplicate natural 

 conditions, Schmidt stretched collodion membranes over one side of glass 

 rings. Copper hydroxide or bordeaux mixture in agar was placed on the 

 underside of the membranes. The rings were divided into two lots, and to 

 one of the lots sugar was added. On the outside of the membranes, spores 

 of Botrytis, Monilia, or Fusicladium were sown, along with the fungicide. 

 With the copper hydroxide, all the spores germinated freely while in con- 

 tact with the copper-hydroxide particles, either with or without sugar. 

 With the bordeaux mixture, however, with or without sugar, there was 

 restricted germination, though any germination or subsequent growth was 

 slightly better where sugar was added. This experiment was further 

 modified and set up in six series. Series 1 and 2 consisted of watch glasses, 

 series 1 containing 2 per cent of copper hydroxide, and series 2 containing 

 2 per cent of bordeaux mixture, in distilled water. A trace of sugar was 

 added to each. Series 3 and 4 were glass slides, sprayed, in the case of 

 series 3 with 2 per cent of copper hydroxide, and in the case of series 4 

 with 2 per cent of bordeaux mixture. These were allowed to dry in the 

 air. Series 5 and 6 consisted of glass rings over which the collodion mem- 

 brane was stretched. In series 5 a little copper hydroxide was rubbed 

 over the surface of the membrane, and on the inside a paste of 2 per cent 

 of copper hydroxide with a trace of sugar was added. Series 6 was treated 

 in the same way except that bordeaux mixture was used instead of copper 

 hydroxide. Spores of Botrytis were sown on all six, the whole series was 

 placed in moist chambers, and the spores were allowed to germinate for 

 six days. The results were as follows: series 1,100 per cent germination: 

 series 2, 20 per cent; series 3, 100 per cent; series 4, 2 per cent; series 5, 

 100 per cent; series 6, per cent; control, 100 per cent. 



In a final test, Schmidt found that Botrytis and Aspergillus germinated 

 only very poorly in lime water. However, limewater apparently did not 

 hinder the germination of Trichothecium spores. 



Schmidt concludes from his studies that there is no exosmosis of sub- 

 stances from the spores which promotes the solution of bordeaux mixture 

 or of copper hydroxide. He concludes also that bordeaux mixture is more 

 toxic than copper hydroxide, and that the fungicidal action of bordeaux 

 mixture is due to the combined influence of the copper brought into solu- 

 tion by the carbonic acid of the atmosphere, and the repressive alkalinity 

 of the mixture. 



Schmidt did not demonstrate the repressive alkalinity of bordeaux mix- 

 ture toward all his spores. Apparently, he assumes that the copper of 

 bordeaux mixture is in the form of copper hydroxide. The copper hydrox- 

 ide employed was very evidently soluble in distilled water to a very appreci- 

 able extent, since Schmidt used the potassiuni-ferrocyanide test, which is 

 not very delicate. In the two last-described experiments a possible solvent 



